Conventionally, a CMOS transistor including a N channel MOSFET and a P channel MOSFET is used for a switching device in an analog circuit or the like. A SiC semiconductor device also provides a CMOS transistor. However, in the SiC semiconductor device, an electron mobility and a hole mobility are largely different from each other. Thus, in the CMOS transistor, it is necessary to adjust an area of each of the P channel MOSFET and the N channel MOSFET so as to equalize channel mobility of the electron and the hole.
FIG. 20A shows a graph of temperature dependency of an electron mobility at various impurity concentrations of a channel layer in 6H—SiC, and FIG. 20B shows a graph of temperature dependency of an electron mobility at various impurity concentrations of a channel layer in 4H—SiC. Further, FIG. 21 shows a relationship between a hole mobility and an acceptor density in each of 6H—SiC and 4H—SiC. As shown in FIGS. 20A to 21, for example, although the electron mobility at 100K reaches three figures, the hole mobility is around two figures. Thus, the electron mobility is about ten times larger than the hole mobility. When the CMOS transistor having a N channel MOSFET and a P channel MOSFET is made of SiC, the area of the P channel MOSFET should be ten times larger than the area of the N channel MOSFET in order to equalize the electron mobility and the hole mobility. Accordingly, when the CMOS transistor is formed from a SiC substrate, it is necessary to increase the dimensions of the CMOS transistor.
In a HEMT made of semiconductor material such as GaN, a structure having a combination of an element operated in a depletion mode and an element operated in an enhanced mode is disclosed in US Patent Application Publication No. 2005/0110054. Here, the depletion mode is defined as D mode, and the enhanced mode is defined as E mode. The channel mobility of the D mode element is equal to the channel mobility of the E mode element since the device does not include the N channel MOSFET and the P channel MOSFET. However, it is difficult to form a certain analog circuit in a semiconductor device including a E mode element and a D mode element. In this case, it is not necessary to adjust the area of the D mode element and the E mode element to equalize the channel mobility. Specifically, the area of the D mode element is equal to the area of the E mode element.
However, in the SiC device, there is no disclosure to form the D mode element and the E mode element in the same substrate. Accordingly, it is required to form the SiC semiconductor device having the D mode element and the E mode element in the same substrate.
Here, although the semiconductor device has the D mode element and the E mode element in the same substrate, it is also required for other materials to form a semiconductor device having a D mode element and a E mode element in the same substrate.